This invention relates generally to puffer type gas circuit breakers and, more particularly, to a puffer type gas circuit breaker having an improved breaking structure and to a contact cover and an insulated nozzle of this breaker.
Ordinarily, in a puffer type gas circuit breaker, arc extinguishing gas in a puffer chamber which is highly compressed and not heated excessively is blown to an arc generated between separated contacts to extinguish the arc in a linked relationship with the operation of disconnecting the contacts. For this operation, it is necessary that the arc extinguishing gas is suitably pressurized and is efficiently blown to the arc.
Japanese Patent Examined Publication No. 52-21701 and Japanese Utility Model Unexamined Publication No. 59-187043 disclose breakers of this kind. FIGS. 12 and 13 show breaking sections of these breakers.
In the breaker shown in FIG. 12, a flow straightening member 89 is provided in a gas flow passage section of an insulated nozzle 87.
FIG. 14 shows the change in the sectional area of the gas flow passage in the insulated nozzle 87 of this breaker in the gas flowing direction, and FIG. 15 shows the change in pressure in the gas flowing direction.
In FIGS. 14 and 15, the abscissas indicate positions a to e shown in FIG. 12, the ordinate of FIG. 14 represents gas flow passage sectional area S and the ordinate of FIG. 15 represents pressure P.
Referring to FIG. 14, the change in the sectional area in the case where the flow straightening member 89 is provided is as represented by a characteristic curve shown as broken line A, and the change in the sectional area in the case where the flow straightening member 89 is not provided is as represented by a characteristic curve shown as solid line B. Referring to FIG. 15, the change in the pressure in the insulated nozzle in the case where the flow straightening member 89 is provided is as represented by a characteristic curve C, and the change in the pressure in the insulated nozzle in the case where the flow straightening member 89 is not provided is as represented by a characteristic curve D.
Also, according to IEEE Transactions of power Apparatus and Systems, Vol. PAS-98, No. 3 May/June 1979 (p. 731 to 737), a temperature of the gas E in the insulated nozzle of the conventional gas breaker shown in FIG. 12 is excessively higher than a suitable gas temperature F since a volume in the insulated nozzle is decreased by the straightening member mounted therein, resulting in failure to set a suitable gas temperature as shown in FIG. 16. The same can also be said with respect to the insulated nozzle shown in FIG. 13. An extinguishing gas-pressure in a puffer-chamber is increased by heating with arc energy occurring in the chamber FIG. 13.